Comparative effects of oral administration of trimethoprim/sulphadiazine or oxytetracycline on the faecal flora of horses

Abstract

A study was carried out on the bacteriological faecal flora of horses before and after oral doses of oxytetracycline or trimethoprim plus sulphadiazine. Administration of oxytetracycline was rapidly followed by large increases in counts of coliforms. Bacteroides and Streptococcus species, the disappearance of Veillonella species, the appearance of Clostridium perfringens type A in large numbers and the accumulation of watery fluid in the rectal contents. These changes were not seen following administration of trimethoprim-sulphadiazine and it was concluded that oral treatment of horses with this combination was unlikely to be accompanied by the hazard of inducing colitis.

Antimicrobial associated diarrhoea in the horse. Part 1: Overview, pathogenesis and risk factors

“…Equine AAD may be associated with the initiation or cessation of antimicrobial therapy (Magdesian et al 1997;Gustafsson 2004). AAD may begin within 24 h of administering a single dose of antimicrobial, but most commonly occurs in the first few days after the start of treatment (Andersson et al 1971;Cook 1973;White and Prior 1982;Staempfli et al 1992;Ensink et al 1996;Gustafsson et al 1997;Prescott et al 1988;Stratton-Phelps et al 2000). Weese (2000) reported that diarrhoea commenced on average 5.7 days after the start of treatment; however, the onset ranged from one day after the start of treatment to 7 days after cessation of treatment.…”

“…While coliforms are not considered to be a cause of equine AAD, several studies have reported alterations in faecal coliform numbers during antimicrobial treatment. Increased faecal coliform counts, which are believed to reflect antimicrobial-induced impairment of colonisation resistance (Vollaard and Clasener 1994), have been associated with administration of oxytetracycline (Andersson et al 1971;White and Prior 1982) and erythromycin and rifampicin . In contrast, administration of trimethoprim/sulphonamide transiently reduced faecal coliform numbers (White and Prior 1982;Gustafsson et al 1999).…”

Application of the lactose13C‐ureide breath test for measurement of equine orocaecal transit time

“…Although oral trimethoprim did not have a significant effect on equine faecal flora (White and Prior 1982), the precise effect of antibiotic administration on LUBT test efficacy has not been determined in any species. Specific disorders in which intestinal anaerobes are increased in number, such as equine grass sickness, might also prove unsuitable for test application, and have yet to be investigated.…”

Acute colitis in adult horses. A review with emphasis on aetiology and pathogenesis

“…Large increases in faecal counts of Cl. perfringens type A, StreptoCoccus spp., and coliforms were reported after oxy- tetracycline administration (35,96). Additionally, White and Prior described elevated counts of Bacteroides spp.…”

“…and disappearance of Veillonella spp. in the faeces after oral dosing with oxytetracycline (96). However, changes in the faecal flora may occur in diarrhoeic horses without a history of antibiotic treatment (32).…”